rx 480 display ports not working only hdmi

On my RX 480 the HDMI port works fine but when I plug any monitor into the Display port I am getting no signal. This only happens intermittently. Sometimes the DPs work but most of the time I can't connect a second display. This is a big problem as I just purchased a Vive and it has to run through the HDMI port leaving just the display ports for my monitor. HELP